1. Technical Field
The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device, and particularly to a semiconductor device having a ridge and a method of manufacturing the semiconductor device.
2. Related Art
There has been proposed is a compound semiconductor device in which a stripe-shaped ridge is formed on a surface of a p-side semiconductor layer of a compound semiconductor device, and a part of an active layer below the ridge is designated as an optical waveguide region. In such a compound semiconductor device, generally, a stripe-shaped ridge is formed on a surface of a compound semiconductor layer stacked on a substrate, and an electrode is electrically connected on the stripe-shaped ridge.
Typical examples of such a compound semiconductor include a group III-V compound semiconductor, in which, a compound semiconductor having a desired composition ratio can be obtained by using one or a plurality of group III elements or group V elements. Among those, as a semiconductor laser capable of emitting light from ultraviolet region to visible light region including green region, a semiconductor laser using a nitride semiconductor such as InAlGaN has been extensively studied.
For example, in a case where a material such as GaAs is used, due to its low contact resistivity, its effects on the laser operating characteristics is hardly expected even if the contact area between the upper surface of the stripe-shaped ridge and the electrode is changed, and a meaningful increase in laser operating voltage is unlikely to occur. Whereas, in a case where a material made of a nitride semiconductor such as GaN is used, due to its higher contact resistivity compared to that of GaAs, the contact resistivity between the electrode and the upper surface of the ridge may be increased according to a change in the contact area between the upper surface of the ridge and the electrode, which may results in increase in laser operating voltage.
In a case where the width of the ridge is increased in order to prevent increase in the contact resistance between the electrode and the upper surface of the ridge, the resulting laser beam will be a multimode laser beam. Even in an application in which a semiconductor device capable of emitting multimode laser beam can be used, the area of the electrode is increased by increasing the ridge width, so that absorption of laser beam at the electrode may generate a problem. An increase in loss due to absorption of laser beam at the electrode as described above may result in decrease in the slope efficiency.
JP 2004-22989A discloses formation of an upper electrode layer and a ridge stripe, in which, an upper electrode layer (10) is formed on a stacked layer structure (100) of a nitride gallium-based compound semiconductor, and a photoresist (40) for stripe is disposed thereon, then, the upper electrode layer and the ridge stripe is formed by using the photoresist as a mask.
JP 2004-119772A discloses formation of a ridge 109a, in which a stacked layer pattern of a SiO2 layer 4 and a ZrO2 layer 5, and the ridge 109a is formed by way of dry etching using the ZrO2 layer 5 as a mask. Next, after depositing a ZrO2 film on the entire surface, the stacked layer pattern described above is used as a mask for liftoff to selectively leave the ZrO2 film 7a at the both sides of the ridge 109a.
JP 2008-98349A discloses formation of a ridge, in which a stacked layer mask part which is made of three layers and has a stripe-shaped pattern is disposed and a ridge part is formed using the stacked layer mask part as a mask. Next, only the mask part at the second sub-layer of the stacked layer mask part is etched from the side surface to form a neck part in the stacked layer mask part, then an insulating film is vapor-deposited on the entire upper surface of this condition. Next, the stacked layer mask part is dissolved to liftoff the insulating layer disposed on the surface of the stacked layer mask part, and an opening of the insulating layer is defined in the upper surface of the ridge part.